. >> as president obama has said, the fbi is investigating this as an act of terrorism and the full force of the federal government will support the response and the investigation. >> investigators now believe the explosives were packed into pressure cookers. these nangle pieces of metal are all that remain. inse parts have been used homemade bombs by extremist groups before. they also recovered a circuit board, which is being examined, and a backpack, which was being used to hide the devices. we now know that three people died. two young women and an 8-year- old boy. others have terrible wounds. vigils have been held again across the city this evening. it is a city still bewildered by what happened these two were in the crowd when the bomb went off. moments later, he called his mom saying, i've been hurt, really bad. boththers both frost -- lost a leg. -- the brothers both lost a leg. >> one will cry and then the other one will. it is heartbreaking. victims have been identified. krystle campbell was one of those killed. her mother paid tribute to her. >> i cannot leave this has happened.